I would say the best way to get that kind of bass drop sound is by using the filter envelope to create a pitch drop in an oscilator, very easy to program on the virus.
The tone is probably good enough with a sine wave, maybe saturate it a bit, then employ the Pitch to filter envelope, or through the matrix, then tweak the amount, keep the Attack at 0, and bringing up the Decay will create the pitch drop lenght.
